Alveolar soft part sarcoma is a rare tumour that mostly affects young female patients. Most published literature involves isolated cases or small case series. We report the case of a 23-year-old woman who presented with a fast-growing, isolated alveolar soft part sarcoma of the left calf. She had no co-morbidities and was 22 weeks pregnant at the time of presentation. Immunohistochemical analysis of the tumour revealed it to be positive for progesterone receptors. Wide excision was performed, with no local recurrence or systemic spread at six-month follow-up. The fact that the tumour expressed progesterone receptors, combined with previous reports of disease progression during pregnancy, raises the possibility of a hormonal contribution to the pathogenesis. This raises the possibility for novel treatment strategies and warrants further investigation.